Microporous filter media, filtration systems containing same, and methods of making and using

ABSTRACT

The invention is directed to a microbiological interception enhanced filter medium, preferably having an adsorbent prefilter located upstream from the filter medium. Preferably, the prefilter is adapted to remove natural organic matter in an influent prior to the influent contacting the microbiological interception enhanced filter medium, thereby preventing loss of charge on the filter medium. The microbiological interception enhanced filter medium is most preferably comprised of fibrillated cellulose fibers, in particular, lyocell fibers. At least a portion of the surface of the at least some of the fibers have formed thereon a microbiological interception enhancing agent comprising a cationic metal complex. A filter medium of the present invention provides greater than about 4 log viral interception, and greater than about 6 log bacterial interception.

This application claims priority from U.S. Provisional ApplicationSerial No. 60/354,062 filed on Jan. 31, 2002.

The present invention is directed to filter media having microbiologicalinterception capability, filtration systems containing such filtermedia, and methods of making and using same.

Modern consumer water filters often provide “health claims” includingreduction of particulates, heavy metals, toxic organic chemicals, andselect microbiological threats. These filtration systems have been ableto intercept microorganisms such as Cryptosporidium and Giardia usingroughly 1.0 micron structures. However, in order to providemicrobiological interception of even smaller microbiological threatssuch as viruses, a filter medium having a sub-micron microporousstructure is required. Prior art filtration systems often attempt toachieve broad microbiological interception using filter media withinsufficiently small pore size and with poor physical integrity. Thebalance between the necessary pore structure required for successfulmicrobiological interception and satisfactory filter performance has notbeen achieved. In addition, prior art systems did not provide devicescapable of operating in the presence of “interferences” consisting ofsubstances that cause a loss of filtration performance.

SUMMARY OF THE INVENTION

The present invention is directed to, in a first aspect, a filter mediumcomprising: a microporous structure having a mean flow path of less thanor equal to about 1 micron; and a microbiological interception enhancingagent comprising a cationic metal complex capable of imparting apositive charge on at least a portion of the microporous structure.

In another aspect, the present invention is directed to a compositefilter medium comprising: an adsorbent prefilter having immobilizedtherein a material capable of removing charge-reducing contaminants; amicroporous structure, disposed downstream from the adsorbent layer,comprising a plurality of nanofibers, the microporous structure having amean flow path of less than about 0.6 micron; and a microbiologicalinterception enhancing agent comprising a silver-cationicmaterial-halide complex having a high charge density, coated on at leasta portion of a surface of at least some of the plurality of fibers ofthe microporous structure.

In yet another aspect, the present invention is directed to a filtersystem comprising: a granular bed of particles capable of removingcharge-reducing contaminants; a microporous structure, disposeddownstream from the granular bed, having a mean flow path of less thanabout 0.6 micron; and a microbiological interception enhancing agentcomprising a silver-cationic material-halide complex having a highcharge density, coated on at least a portion of a surface of themicroporous structure.

In still yet another aspect, the present invention is directed to afilter system comprising: a solid composite block comprising a materialcapable of removing charge-reducing contaminants; a microporousstructure, disposed downstream from the block, having a mean flow pathof less than about 2.0 microns; and a microbiological interceptionenhancing agent comprising a silver-cationic material-halide complexhaving a high charge density, coated on at least a portion of a surfaceof the microporous structure.

In still yet another aspect, the present invention is directed to aprocess of making a filter medium comprising the steps of: providing amicroporous structure having a mean flow path of less than about 1micron; and coating at least a portion of the microporous structure witha microbiological interception enhancing agent, the microbiologicalinterception enhancing agent comprising a cationic metal complex capableof imparting a positive charge on at least a portion of the microporousstructure.

In a further aspect, the present invention is directed to a process formaking a filter medium comprising the steps of: providing a plurality ofnanofibers; coating at least a portion of a surface of at least some ofthe plurality of nanofibers with a microbiological interceptionenhancing agent, the microbiological intercepting agent comprising acationic metal complex; and forming the fibers into a microporousstructure having a mean flow path of less than about 1 micron.

In still a further aspect, the present invention is directed to aprocess for making a filter medium comprising the steps of: providing aplurality of polymer nanofibers; coating at least a portion of a surfaceof at least some of the plurality of polymer nanofibers with amicrobiological interception enhancing agent, the microbiologicalintercepting agent comprising a cationic metal complex; and forming amicroporous structure having a mean flow path of less than about 1micron.

In still a further aspect, the present invention is directed to aprocess for making a filter medium comprising the steps of: providing aplurality of cellulose nanofibers; coating at least a portion of asurface of at least some of the plurality of cellulose fibers with amicrobiological interception enhancing agent, the microbiologicalintercepting agent comprising a cationic metal complex; and forming amicroporous structure having a mean flow path of less than about 1micron.

In still yet a further aspect, the present invention is directed to aprocess of making a filter medium comprising the steps of: providing amembrane having a mean flow path of less than about 1 micron; andcoating at least a portion of the membrane with a microbiologicalinterception enhancing agent, the microbiological interception enhancingagent comprising a cationic metal complex capable of imparting apositive charge on at least a portion of the membrane.

In still yet a further aspect, the present invention is directed to aprocess for making a filter medium comprising the steps of: providing aplurality of nanofibers; coating at least a portion of a surface of atleast some of the plurality of the nanofibers with a microbiologicalinterception enhancing agent, the microbiological intercepting agentcomprising a silver-amine-halide complex having a medium to high chargedensity and a molecular weight greater than 5000 Daltons; and forming amicroporous structure having a mean flow path of less than or about 0.6microns.

In still yet a further aspect, the present invention is directed to aprocess for making a filter system comprising the steps of: providing anadsorbent prefilter comprising a material capable of removingcharge-reducing contaminants from an influent, wherein the material isimmobilized into a solid composite block; providing a plurality ofnanofibers; coating at least a portion of a surface of at least some ofthe plurality of the nanofibers with a microbiological interceptionenhancing agent, the microbiological intercepting agent comprising asilver-amine-halide complex having a medium to high charge density and amolecular weight greater than 5000 Daltons; and forming a microporousstructure having a mean flow path of less than or about 0.6 microns.

In still yet a further aspect, the present invention is directed to amethod of removing microbiological contaminants in a fluid comprisingthe steps of: providing a filter medium having a microporous structurehaving a mean flow path of less than about 1 micron, the microporousstructure having coated on at least a portion thereof a microbiologicalinterception enhancing agent comprising a cationic metal complex whereinthe cationic material has a medium to high charge density and amolecular weight greater than about 5000 Daltons; contacting the fluidto the filter medium for greater than about 3 seconds; and obtaining atleast about 6 log reduction of microbiological contaminants smaller thanthe mean flow path of the filter medium, that pass through the filtermedium.

In still yet a further aspect, the present invention is directed to agravity-flow filtration system for treating, storing, and dispensingfluids comprising: a first reservoir for holding a fluid to be filtered;a filter medium in fluid communication with the first reservoir, thefilter medium comprising a microporous structure with a mean flow pathof less than about 1 micron, and wherein the filter medium is so treatedas to provide at least about 4 log reduction of microbiologicalcontaminants smaller than the mean flow path of the filter medium; and asecond reservoir in fluid communication with the filter medium forcollecting a filtered fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularity in theappended claims. The figures are for illustration purposes only and arenot drawn to scale. The invention itself, however, both as toorganization and method of operation, may best be understood byreference to the description of the preferred embodiment(s) that followstaken in conjunction with the accompanying drawings in that:

FIG. 1 is a side plan view of a filter incorporating the filter media ofthe present invention.

FIG. 2 is a cross sectional view of the filter of FIG. 1 taken at lines2—2.

FIG. 3 is a front plan view of an exemplary gravity flow filtrationsystem of the present invention.

FIG. 4 is a perspective view of another exemplary gravity flowfiltration system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In describing the preferred embodiment of the present invention,reference will be made herein to FIGS. 1 to 4 of the drawings in thatlike numerals refer to like features of the invention. Features of theinvention are not necessarily shown to scale in the drawings.

Definitions

As used herein, “absorbent” shall mean any material that is capable ofabsorbing impurities primarily by drawing the impurities into its innerstructure.

As used herein, “adsorbent” shall mean any material that is capable ofadsorbing impurities primarily by physical adsorption to its surface.

As used herein, “adsorbent filter medium” or “adsorbent prefiltrationmedium” shall mean a filter medium made with an adsorbent such as, forexample, activated carbon. Exemplary of an adsorbent filter medium isPLEKX®, commercially available from KX Industries, L.P. of Orange, Conn.

As used herein, “binder” shall mean a material used principally to holdother materials together.

As used herein, “Canadian Standard Freeness” or “CSF” shall mean a valuefor the freeness or drainage rate of pulp as measured by the rate that asuspension of pulp may be drained. This methodology is well known to onehaving skill in the paper making arts.

As used herein, “composite filter medium” shall mean a filter mediumthat combines a prefilter, an adsorbent prefiltration medium, and themicrobiological interception enhanced filter medium of the presentinvention, into a single composite structure. In some cases, theprefilter may be absent or its function assumed by the adsorbentprefiltration medium.

As used herein, “contaminant reduction” shall mean attenuation of animpurity in a fluid that is intercepted, removed, or rendered inactive,chemically or biologically, in order to render the fluid safer as, forexample for human use, or more useful, as in industrial applications.

As used herein, “fiber” shall mean a solid that is characterized by ahigh aspect ratio of length to diameter of, for example, several hundredto one. Any discussion of fibers includes whiskers.

As used herein, “filter medium” shall mean a material that performsfluid filtration.

As used herein, “fluid” shall mean a liquid, gas, or combinationthereof.

As used herein, “forming” shall mean converting a loose, unstructuredsubstance into a cohesive, uniform structure. For example, theconversion of loose fibers into a paper.

As used herein, “intercept” or “interception” are taken to meaninterfering with, or stopping the passage of, so as to affect, remove,inactivate or influence.

As used herein, “log reduction value” or “LRV” shall mean the log₁₀ ofthe number of organisms in the influent divided by the number oforganisms in the effluent of a filter.

As used herein, “membrane” shall mean a porous medium wherein thestructure is a single continuous solid phase with a continuous porestructure.

As used herein, “microbiological interception enhanced filter medium”shall mean a filter medium having a microporous structure where at leasta portion of its surface is treated with a microbiological interceptionenhancing agent.

As used herein, “microorganism” shall mean any living organism that maybe suspended in a fluid, including but not limited to bacteria, viruses,fungi, protozoa, and reproductive forms thereof including cysts andspores.

As used herein, “microporous structure” shall mean a structure that hasa mean flow path less than about 2.0 microns, and often less than about1.0 micron.

As used herein, “nanofiber” shall mean a fiber having a diameter lessthan about 3.0 millimeters.

As used herein, “natural organic matter” or “NOM” shall mean organicmatter often found in potable or non-potable water, a portion of whichreduces or inhibits the zeta potential of a positively charged filtermedium. Exemplary of NOM are polyanionic acids such as, but not limitedto, humic acid and fulvic acid.

As used herein, “nonwoven” means a web or fabric or other medium havinga structure of individual fibers that are interlaid, but not in a highlyorganized manner as in a knitted or woven fabric. Nonwoven websgenerally may be prepared by methods that are well known in the art.Examples of such processes include, but are not limited to, and by wayof illustration only, meltblowing, spunbonding, carding, and air laying.

As used herein, “paper” or “paper-like” shall mean a generally flat,fibrous layer or mat of material formed by a wet laid process.

As used herein, “particle” shall mean a solid having a size range fromthe colloidal to macroscopic, and with no specific limitation on shape,but generally of a limited length to width ratio.

As used herein, “prefilter” shall mean a filter medium generally locatedupstream from other filtration layers, structures or devices and capableof reducing particulate contaminants prior to the influent contactingsubsequent filtration layers, structures or devices.

As used herein, “sheet” shall mean a roughly two-dimensional structurehaving a length and a width that are significantly greater than itsthickness.

As used herein, “whisker” shall mean a filament having a limited aspectratio and intermediate between the aspect ratio of a particle and afiber. Any discussion of fibers includes whiskers.

The Microbiological Interception Enhanced Filter Medium

A filter medium of the present invention includes a microporousstructure that provides microbiological interception capability using acombination of an appropriate pore structure and a chemical treatment.The microporous structure comprises any material that is capable ofhaving a mean flow path of less than about 2.0 microns. Preferably, themicroporous structure comprises nanofibers formed into a nonwoven orpaper-like structure, but may include whiskers, or be a membrane. Thetight pore structure of the microbiological interception enhanced filtermedium of the present invention provides short diffusion distances fromthe fluid to the surface of the filter medium. The chemical treatmentprocess used to treat the surface of the microporous structure utilizesa synergistic interaction between a cationic material and a biologicallyactive metal, that when combined, provide broad-spectrum reduction ofmicrobiological contaminants on contact. The charge provided by thecationic material to the filter medium aids in electro-kineticinterception of microbiological contaminants, while the tight porestructure provides a short diffusion path and, therefore, rapiddiffusion kinetics of contaminants in a flowing fluid to the surface ofthe microporous structure. The microporous structure also providessupplemental direct mechanical interception of microbiologicalcontaminants. Due to the dominant role of diffusion for the interceptionof extremely small particles, there is a direct correlation between thelog reduction value of viral particles and the contact time of theinfluent within the filter medium, rather than a dependence upon thethickness of the filter medium.

Characteristics of the Microbiological Interception Enhanced FilterMedium

In order to provide full microbiological interception capability, themicrobiological interception enhanced filter medium of the presentinvention has a mean flow path of less than about 2 microns, andpreferably less than or equal to about 1 micron, and more preferablyless than or equal to about 0.6 microns. The volume of themicrobiological interception enhanced filter medium of the presentinvention compared to the flow rate of fluid through the filter mediummust be sufficient to provide a contact time adequate for thecontaminants to diffuse to the surface of the filter medium. To provideenhanced electro-kinetic interception of microorganisms, of which themajority are negatively charged, under most conditions, themicrobiological interception enhanced filter medium has a positive zetapotential generally greater than about +10 millivolts at pH values ofabout 6 to about 7, and retains a net positive zeta potential at pHvalues of about 9 or greater.

Natural organic matter (NOM), such as polyanionic acids, i.e., humicacid or fulvic acid, that may reduce or remove the charge on themicrobiological interception enhanced filter medium, is preferablyprevented from contacting the charged microporous structure through theuse of an adsorbent prefilter that substantially removes the NOM. Whenused in the context of a gravity-flow water filtration system, it ispreferable that the microbiological interception enhanced filter mediumbe made with hydrophilic materials to provide good, spontaneouswettability. Alternatively, in other applications, the microbiologicalinterception enhanced filter medium may be treated to provide either ahydrophilic or hydrophobic characteristic as needed. It is possible thatthe microbiological interception enhanced filter medium can have bothpositively and negatively charged and uncharged regions, and/orhydrophilic and hydrophobic regions. For example, the negatively chargedregions can be used to enhance the interception of less commonpositively charged contaminants and uncharged hydrophobic regions can beused to provide enhanced interception of contaminants that are attractedto hydrophobic surfaces.

The Fibers/Whiskers or Particulate Ingredients

The microbiological interception enhanced filter medium of the presentinvention includes a microporous structure that may include a pluralityof nanofibers, including whiskers or micro-particulate ingredients, oforganic and inorganic materials including, but not limited to, polymers,ion-exchange resins, engineered resins, ceramics, cellulose, rayon,ramie, wool, silk, glass, metal, activated alumina, carbon or activatedcarbon, silica, zeolites, diatomaceous earth, activated bauxite,fuller's earth, calcium hydroxyappatite, other adsorbent materials, orcombinations thereof. Combinations of organic and inorganic fibersand/or whiskers or micro-particules are contemplated and within thescope of the invention as for example, glass, ceramic, or metal fibersand polymeric fibers may be used together with very small particlesincorporated into the microporous structure.

When produced by a wet laid process from nanofibers such as cellulose orpolymer fibers, such fibers should also have a Canadian StandardFreeness of less than or equal to about 100, and most preferably lessthan or equal to about 45. Preferably, a significant portion of thefibers should have a diameter less than or equal to about 1000nanometers, more preferably less than or equal to about 400 nanometers,and fibers less than or equal to about 250 nanometers in diameter aremost preferred. It is preferable to chop the fibers to a length of about1 millimeter to about 8 millimeters, preferably about 2 millimeters toabout 6 millimeters, and more preferably about 3 millimeters to about 4millimeters. Fibrillated fibers are most preferred due to theirexceptionally fine dimensions and potentially low cost.

Preferably, fibrillated synthetic cellulose fibers, processed inaccordance with the present invention, can produce an ultra-fine,hydrophilic microporous structure for use as the microbiologicalinterception enhanced filter medium of the present invention. Suchfibrillated cellulose fibers can be made by direct dissolution andspinning of wood pulp in an organic solvent, such as an amine oxide, andare known as lyocell fibers. Lyocell fibers have the advantage of beingproduced in a consistent, uniform manner, thus yielding reproducibleresults, which may not be the case for, for example, natural cellulosefibers. Further, the fibrils of lyocell are often curled. The curlsprovide a significant amount of fiber entanglement, resulting in afinished filter medium with high dry strength and significant residualwet strength. Furthermore, the fibrillated lyocell fibers may beproduced in large quantities using equipment of modest capital cost. Itwill be understood that fibers other than cellulose may be fibrillatedto produce extremely fine fibrils, such as for example, artificialfibers, in particular, acrylic or nylon fibers, or other naturalcellulosic materials. Combinations of fibrillated and non-fibrillatedfibers may be used in the microporous structure.

Membranes

The microbiological interception enhanced filter medium of the presentinvention can comprise a membrane of organic or inorganic compositionincluding, but not limited to, polymers, ion-exchange resins, engineeredresins, ceramics, cellulose, rayon, ramie, wool, silk, glass, metal,activated alumina, activated carbon, silica, zeolites, diatomaceousearth, activated bauxite, fuller's earth, calcium hydroxyappatite,titanates and other materials, or combinations thereof. Combinations oforganic and inorganic materials are contemplated and within the scope ofthe invention. Such membranes may be made using methods known to one ofskill in the art.

The Microbiological Interception Enhancing Agent

The nanofibers or membrane that make up the microporous structure arechemically treated with a microbiological interception enhancing agentcapable of creating a positive charge on the microbiologicalinterception enhanced filter medium. A cationic metal complex is formedon at least a portion of the surface of at least some of the fibers orthe membrane by treating the fibers or membrane with a cationicmaterial. The cationic material may be a small charged molecule or alinear or branched polymer having positively charged atoms along thelength of the polymer chain.

If the cationic material is a polymer, the charge density is preferablygreater than about 1 charged atom per about every 20 Angstroms,preferably greater than about 1 charged atom per about every 12Angstroms, and more preferably greater than about 1 charged atom perabout every 10 Angstroms of molecular length. The higher the chargedensity on the cationic material, the higher the concentration of thecounter ion associated therewith. A high concentration of an appropriatecounter ion can be used to drive the precipitation of a cationic metalcomplex. The cationic material should consistently provide a highlypositively charged surface to the microporous structure as determined bya streaming or zeta potential analyzer, whether in a high or low pHenvironment. Zeta or streaming potentials of the microporous structureafter treatment with a high molecular weight charged polymer can begreater than about +10 millivolts, and often up to about +23 millivoltsat a substantially neutral pH.

The cationic material includes, but is not limited to, quaternizedamines, quaternized amides, quaternary ammonium salts, quaternizedimides, benzalkonium compounds, biguanides, cationic aminosiliconcompounds, cationic cellulose derivatives, cationic starches,quaternized polyglycol amine condensates, quaternized collagenpolypeptides, cationic chitin derivatives, cationic guar gum, colloidssuch as cationic melamine-formaldehyde acid colloids, inorganic treatedsilica colloids, polyamide-epichlorohydrin resin, cationic acrylamides,polymers and copolymers thereof, combinations thereof, and the like.Charged molecules useful for this application can be small moleculeswith a single charged unit and capable of being attached to at least aportion of the microporous structure. The cationic material preferablyhas one or more counter ions associated therewith which, when exposed toa biologically active metal salt solution, cause preferentialprecipitation of the metal in proximity to the cationic surface to forma cationic metal precipitate.

Exemplary of amines may be pyrroles, epichlorohydrin derived amines,polymers thereof, and the like. Exemplary of amides may be thosepolyamides disclosed in International Patent Application No. WO01/07090, and the like. Exemplary of quaternary ammonium salts may behomopolymers of diallyl dimethyl ammonium halide, epichlorohydrinderived polyquaternary amine polymers, quaternary ammonium salts derivedfrom diamines and dihalides such as those disclosed in U.S. Pat. Nos.2,261,002, 2,271,378, 2,388,614, and 2,454,547, all of which areincorporated by reference, and in International Patent Application No.WO 97/23594, also incorporated by reference,polyhexamethylenedimethylammonium bromide, and the like. The cationicmaterial may be chemically bonded, adsorbed, or crosslinked to itself orto the fiber or membrane.

Furthermore, other materials suitable for use as the cationic materialinclude BIOSHIELD® available from BioShield Technologies, Inc.,Norcross, Ga. BIOSHIELD® is an organosilane product includingapproximately 5% by weight octadecylaminodimethyltrimethoxysilylpropylammonium chloride and less than 3% chloropropyltrimethoxysilane. Anothermaterial that may be used is SURFACINE®, available from SurfacineDevelopment Company LLC, Tyngsboro, Mass. SURFACINE® comprises athree-dimensional polymeric network obtained by reactingpoly(hexamethylenebiguanide) (PHMB) with4,4′-methlyene-bis-N,N-diglycidylaniline (MBGDA), a crosslinking agent,to covalently bond the PHMB to a polymeric surface. Silver, in the formof silver iodide, is introduced into the network, and is trapped assubmicron-sized particles. The combination is an effective biocide,which may be used in the present invention. Depending upon the fiber andmembrane material, the MBGDA may or may not crosslink the PHMB to thefiber or the membrane.

The cationic material is exposed to a biologically active metal saltsolution such that the cationic metal complex precipitates onto at leasta portion of the surface of at least some of the fibers or the membrane.For this purpose, the metals that are biologically active are preferred.Such biologically active metals include, but are not limited to, silver,copper, zinc, cadmium, mercury, antimony, gold, aluminum, platinum,palladium, and combinations thereof. Most preferred are silver andcopper. The biologically active metal salt solution is preferablyselected such that the metal and the counter ion of the cationicmaterial are substantially insoluble in an aqueous environment to driveprecipitation of the cationic metal complex.

A particularly useful microbiological interception enhancing agent is acationic silver-amine-halide complex. The cationic amine is preferably ahomopolymer of diallyl dimethyl ammonium halide having a molecularweight of about 400,000 Daltons or other quaternary ammonium saltshaving a similar charge density and molecular weight. A homopolymer ofdiallyl dimethyl ammonium chloride useful in the present invention iscommercially available from Nalco Chemical Company of Naperville, Ill.,under the tradename MERQUAT® 100. The chloride counter ion may bereplaced with a bromide or iodide counter ion. When contacted with asilver nitrate solution, the silver-amine halide complex precipitates onat least a portion of the fibers or membrane of the microporousstructure of the filter medium.

The pH of the surrounding solution does affect the zeta potential of themicrobiological interception enhanced filter medium of the presentinvention. An acidic pH will increase the charge on the filter mediumwhile a basic pH will decrease the charge on the filter medium. Under pHconditions typically encountered in potable water, the microbiologicalinterception enhanced filter medium does retain a minimum positivecharge and only at very high pH values does the charge decline belowzero millivolts. Exposure to NOM, such as polyanionic acids, willdecrease the zeta potential of the microbiological interception enhancedfilter medium. This will diminish its microbiological interceptioncapabilities. Therefore, in applications where high levels of NOM arepresent, an adsorbent prefilter capable of removing the NOM extends theuseful life of the microbiological interception enhanced filter medium.

Methods of Making the Microbiological Interception Enhanced FilterMedium

The microbiological interception enhanced filter medium may be made inaccordance with processes known to one of skill in the art. Dry laidprocesses include spun bonding, electrospinning, spinning islands-in-seaprocesses, fibrillated films, melt blowing, and other dry laid processesknown to one of skill in the art. An exemplary dry laid process startswith staple fibers, which can be separated by carding into individualfibers and are then laid together to a desired thickness by anaerodynamic or hydrodynamic process to form an unbonded fiber sheet. Theunbonded fibers can then be subjected to hydraulic jets to bothfibrillate and hydroentangle the fibers. A similar process can beperformed on certain plastic films that when exposed to high pressurejets of water, are converted into webs of fibrillated fibers.

In a preferred wet laid process, a fiber tow is chopped to a specificlength, usually in the range of about 1 millimeter to about 8millimeters, and in particular in the range of about 3 millimeters toabout 4 millimeters. The chopped fibers are fibrillated in a devicehaving characteristics similar to a blender, or on a large scale, inmachines commonly referred to as a “hi-low”, a “beater” or a “refiner”.The fiber is subjected to repetitive stresses, while further choppingand the reduction of fiber length is minimized. As the fibers undergothese stresses, the fibers split as a result of weaknesses betweenamorphous and crystalline regions and the Canadian Standard Freeness(CSF), which is determined by a method well known in the art, begins todecline. Samples of the resulting pulp can be removed at intervals, andthe CSF used as an indirect measure of the extent of fibrillation. Whilethe CSF value is slightly responsive to fiber length, it is stronglyresponsive to the degree of fiber fibrillation. Thus, the CSF, which isa measure of how easily water may be removed from the pulp, is asuitable means of monitoring the degree of fiber fibrillation. If thesurface area is very high, then very little water will be drained fromthe pulp in a given amount of time and the CSF value will becomeprogressively lower as the fibers fibrillate more extensively. Thefibrillated fiber of a given CSF value can be directly used forproducing paper or dewatered on a variety of different devices,including a dewatering press or belt, to produce a dewatered pulp. Thedewatered pulp can be subsequently used to make a wet-laid paper.Generally, for application in the present invention, a pulp with a CSFof below 100 is used, and preferably, the CSF should be less than orequal to about 45.

The pulp is treated with a cationic material in such a manner as toallow the cationic material to coat at least a portion of the surface ofat least some of the fibers thereby imparting a charge on the fibers.Methods of applying the cationic material to the fibers are known in theart and include, but are not limited to, spray, dip, or submergencecoating to cause adsorption, chemical reaction or crosslinking of thecationic material to the surface of the fibers. The treated pulp is thenrinsed in reverse osmosis/deionized (RO/DI) water, partially dewatered,usually under vacuum, to produce a wet lap that can then be exposed to abiologically active metal salt solution. The use of nearly ion-freerinse water causes the counter-ions associated with the cationicmaterial to be drawn tightly against the treated fiber surface and toeliminate unwanted ions that may cause uncontrolled precipitation of thebiologically active metal into sites remote from the cationic surface.

The metal salt solution is infiltrated into the fibers to allowprecipitation of the cationic metal complex on a surface of at least aportion of the fibers. The precipitation accurately deposits a metalcolloid adjacent to the cationic coating because the counter-ionassociated with this coating reacts with the applied metal salt to formcolloidal particles. After sufficient exposure to the biologicallyactive metal salt solution, the fibers can be rinsed and excess water isremoved. Alternatively, the fibers can be directly sent to pulppreparation systems to create a furnish suitable for paper making.

When silver nitrate is used as the metal salt solution, the presence ofprecipitated silver can be confirmed by using a Kratos EDX-700/800 X-rayfluorescence spectrometer available from Kratos Analytical, a ShimadzuGroup Company, Japan.

The microbiological interception enhanced filter medium comprising amembrane may be made in accordance with processes known to one of skillin the art. Raw material for the membrane may be treated prior toforming the membrane or the cationic material may be applied to themembrane material using known methods in the art and similar to thoseused to treat the fiber surfaces.

Additives

The strength of the wet laid fiber sheet, especially when wet, may beimproved with the addition of various additives. It is well known in theart that the addition of epoxy or acrylic or other resins to the papermaking process can provide enhanced wet strength, but thesewater-dispersed resins often cause lower permeability to the finalproduct, especially as fiber size becomes very small. Although theseresins and resin systems can be used in the current invention, it ispreferable to use thermoplastic or thermoset materials known in the art,and in either powder, particulate or fiber form.

Useful binder materials include, but are not limited to, polyolefins,polyvinyl halides, polyvinyl esters, polyvinyl ethers, polyvinylsulfates, polyvinyl phosphates, polyvinyl amines, polyamides,polyimides, polyoxidiazoles, polytriazols, pdlycarbodiimides,polysulfones, polycarbonates, polyethers, polyarylene oxides,polyesters, polyarylates, phenol-formaldehyde resins,melamine-formaldehyde resins, formaldehyde-ureas, ethyl-vinyl acetatecopolymers, co-polymers and block interpolymers thereof, andcombinations thereof. Variations of the above materials and other usefulpolymers include the substitution of groups such as hydroxyl, halogen,lower alkyl groups, lower alkoxy groups, monocyclic aryl groups, and thelike. Other potentially applicable materials include polymers such aspolystyrenes and acrylonitrile-styrene copolymers, styrene-butadienecopolymers, and other non-crystalline or amorphous polymers andstructures.

A more detailed list of binder materials that may be useful in thepresent invention include end-capped polyacetals, such aspoly(oxymethylene) or polyformaldehyde, poly(trichloroacetaldehyde),poly(n-valeraldehyde), poly(acetaldehyde), and poly(propionaldehyde);acrylic polymers, such as polyacrylamide, poly(acrylic acid),poly(methacrylic acid), poly(ethyl acrylate), and poly(methylmethacrylate); fluorocarbon polymers, such as poly(tetrafluoroethylene),perfluorinated ethylene-propylene copolymers,ethylene-tetrafluoroethylene copolymers, poly(chlorotrifluoroethylene),ethylene-chlorotrifluoroethylene copolymers, poly(vinylidene fluoride),and poly(vinyl fluoride); polyamides, such as poly(6-aminocaproic acid)or poly(e-caprolactam), poly(hexamethylene adipamide),poly(hexamethylene sebacamide), and poly(11-aminoundecanoic acid);polyaramides, such as poly(imino-1,3-phenyleneiminoisophthaloyl) orpoly(m-phenylene isophthalamide); parylenes, such as poly-2-xylylene,and poly(chloro-1-xylylene); polyaryl ethers, such aspoly(oxy-2,6-dimethyl-1,4-phenylene) or poly(p-phenylene oxide);polyaryl sulfones, such aspoly(oxy-1,4-phenylenesulfonyl-1,4-phenyleneoxy-1,4-phenyl-eneisopropylidene-1,4-phenylene), andpoly(sulfonyl-1,4-phenylene-oxy-1,4-phenylenesulfonyl4,4′-biphenylene);polycarbonates, such as poly-(bisphenol A) orpoly(carbonyldioxy-1,4-phenyleneisopropylidene-1,4-phenylene);polyesters, such as poly(ethylene terephthalate), poly(tetramethyleneterephthalate), and poly(cyclohexyl-ene-1,4-dimethylene terephthalate)or poly(oxymethylene-1,4-cyclohexylenemethyleneoxyterephthaloyl);polyaryl sulfides, such as poly(p-phenylene sulfide) orpoly(thio-1,4-phenylene); polyimides, such aspoly(pyromellitimido-1,4-phenylene); polyolefins, such as polyethylene,polypropylene, poly(1-butene), poly(2-butene), poly(1-pentene),poly(2-pentene), poly(3-methyl-1-pentene), and poly(4-methyl-1-pentene);vinyl polymers, such as poly(vinyl acetate), poly(vinylidene chloride),and poly(vinyl chloride); diene polymers, such as1,2-poly-1,3-butadiene, 1,4-poly-1,3-butadiene, polyisoprene, andpolychloroprene; polystyrenes; and copolymers of the foregoing, such asacrylonitrilebutadiene-styrene (ABS) copolymers. Polyolefins that may beuseful include polyethylene, linear low density polyethylene,polypropylene, poly(1-butene), poly(2-butene), poly(1-pentene),poly(2-pentene), poly(3-methyl-1-pentene), poly(4-methyl-1-pentene), andthe like.

A range of binder fibers, including polyethylene, polypropylene,acrylic, or polyester-polypropylene or polypropylene-polyethylenebi-component fibers, or others can be used. Certain types of treatedpolyethylene fibers, when properly treated, as described below, areoptimal, and have the additional benefit of not significantlyinterfering with the hydrophilic nature of the resulting filter mediumwhen used in modest volumes. Preferred fiber binder materials mayinclude FYBREL® synthetic fibers and/or SHORT STUFF® EST-8, both ofwhich are polyolefin based. FYBREL® is a polyolefin based synthetic pulpthat is a highly fibrillated fiber and is commercially available fromMitsui Chemical Company, Japan. FYBREL® has excellent thermalmoldability and provides a smooth surface to the filter medium. SHORTSTUFF® EST-8 is commercially available from MiniFibers, Inc.,Pittsburgh, Pa., and is a highly fibrillated, high density polyethylene.

Preferably, the binder material is present in an amount of about 1% toabout 10% by weight, more preferably about 3% to about 6%, and mostpreferably about 5%. It is preferable that the binder material have asoftening point that is significantly lower than a softening point ofthe nanofiber material so that the filter medium can be heated toactivate the binder material, while the microporous structure does notmelt and thereby lose porosity.

One or more additives either in a particulate, fiber, whisker, or powderform may also be mixed with the nanofibers or incorporated into themembrane to aid in adsorption of other contaminants or participate inthe formation of the microporous structure and interception ofmicrobiological contaminants. Useful additives may include, but are notlimited to, metallic particles, activated alumina, activated carbon,silica, polymeric powders and fibers, glass beads or fibers, cellulosefibers, ion-exchange resins, engineered resins, ceramics, zeolites,diatomaceous earth, activated bauxite, fuller's earth, calcium sulfate,other adsorbent materials such as super adsorbent polymers (SAPs), orcombinations thereof. The additives can also be chemically treated toimpart microbiological interception capabilities depending upon theparticular application. Such additives are preferably present in asufficient amount such that the fluid flow in the resultant filtermedium is not substantially impeded when used in filtrationapplications. The amount of additives is dependent upon the particularuse of the filtration system.

Exemplary of a wet laid process includes mixing a pulp of 45 CSFfibrillated lyocell fibers with 5% EST-8 binder fibers and dispersingthe pulp and binder fibers in deionized water with mixing in a blenderto form a furnish with about 1% to about 2% consistency. To this mixtureis added about 3% by weight of MERQUAT® 100, which is briefly dispersedinto the dilute pulp furnish. The cationic material remains in contactwith the pulp for about 4 to about 12 hours until a significant portionhas been adsorbed onto at least a portion of the fibers to impart andmaintain a positive zeta potential on the fibers. Within about eighthours at room temperature, sufficient MERQUAT® is adsorbed to provide apositive zeta potential on the fibers that is greater than about +10millivolts. Next, this pulp is partially dewatered under vacuum andrinsed with deionized water to form a wet lap. A metal salt solution,such as, for example, silver nitrate, in an amount equal to 0.5% byweight of the dry nanofibers, is prepared with deionized water, anduniformly poured over the sheet and allowed to stand for a short time toallow precipitation of the biologically active metal with at least aportion of the counter ion associated with the cationic material.Thereafter, the fibers can be directly used in the production of wetlaid filter medium.

Filtration Systems Utilizing the Microbiological Interception EnhancedFilter Medium

Many types of filtration systems incorporating the current filter mediumcan be imagined. Described below are certain specific embodiments.However, these filtration systems are exemplary and should not beconstrued as restricting the scope of the invention.

Precoat Filtration Systems Including Microbiological InterceptionEnhanced Nanofiber

One filtration system of the present invention that utilizes nanofiberstreated with the microbiological interception enhancing agent, is anindustrial, commercial or municipal filter that uses a precoat appliedto a porous septa. This coating is produced by dispersing particles suchas diatomaceous earth, perlite or fibers as a precoat applied to theporous septa for filtering liquids such as beer, wine, juices, and otherliquids used in the food service or pharmaceutical industry. As theliquid contacts the filter cake, unwanted contaminants are removed whilealso clarifying the liquid. The charged nanofibers not only removenegatively charged contaminants in the liquid much smaller than thepores of the precoat but greatly improve the mechanical interception ofall particles. The nanofibers may be used in conjunction withtraditional precoat ingredients such as diatomaceous earth. Only a smallamount of nanofibers are needed in the precoat, generally about 1.5% toabout 10% by weight, to produce a significant effect. Preferably, ahydrophilic microbiological interception enhanced filter medium is usedin these applications.

Filtration Systems Involving Multiple Layers of Filter Medium

A microbiological interception enhanced filter medium of the presentinvention can include configurations having more than one layer of themicrobiological interception enhanced filter medium. A firstmicrobiological interception enhanced filter medium layer may bepositively charged while a second layer may be negatively charged. Thenegatively charged material can be produced by contacting the nanofiberspulp with a negatively charged compound or material such as apolycarboxylic acid mixed with a small quantity of a crosslinking agentsuch as a glycerine. Heating the nanofibers after soaking in such amixture results in the formation of a coating on the nanofibers ofnegatively charged carboxylic acid polymer crosslinked by the glycerine.The multi-layer microbiological interception enhanced filtration systemis capable of intercepting both positively and negatively chargedmicrobiological targets. Again, in applications where NOM is present, anadsorbent prefilter may be needed to preserve the charge on themicrobiological interception enhanced filter medium.

Filtration Systems with an Adsorbent Prefilter Combined with theMicrobiological Interception Enhanced Filter Medium

A microporous filter medium of the present invention treated with themicrobiological interception enhancing agent may be used as a flat sheetmedium, a pleated medium, or as a spiral wound medium depending upon theapplication and the filter housing design. It may be used for just aboutany type of fluid filtration including water and air.

However, the microbiological interception enhanced filter medium may beless effective in the presence of moderate to high levels of NOM such aspolyanionic humic acid and fulvic acid, due to the decrease and eventualloss of positive charge on the filter medium in the presence of suchacids. Therefore, such applications utilizing the microbiologicalinterception enhanced filter medium alone should be substantially freeof or have low levels of polyanionic acids.

In filtration systems containing the microbiological interceptionenhanced filter medium that may come in contact with fluids that containNOM, it is prudent to use an adsorbent prefilter to remove the NOM inthe influent prior to it contacting the microbiological interceptionenhanced filter medium. Alternatively, the positively charged filtermedium can be formed into a multitude of layers either as a stack ofsheets or by conversion into a structure. Under this type ofarrangement, the outer layers of the filter medium can be sacrificed toremove the NOM, while the inner layers are protected and providelong-term reduction of microbiological contaminants. Additives thatadsorb or absorb NOM may be incorporated into the microporous structure,including anion exchange resins. To avoid this costly loss ofsacrificial material, the following examples describe other alternativemethods for arranging the protection of the filter medium from theeffects of NOM.

1. A Flat Adsorbent Filter Medium as a Prefilter

The microbiological interception enhanced filter medium may be used inconjunction with adsorbent filtration media that serve to intercept NOMinterferences prior to their contact with the charged microbiologicalinterception enhanced filter medium. The microbiological interceptionenhanced filter medium and one or more layers of an adsorbent filtrationmedium may be used as a flat sheet composite, spiral wound together, orpleated together. Such an adsorbent filtration medium may bemanufactured according to U.S. Pat. Nos. 5,792,513 and 6,077,588, aswell as other processes in the prior art. A particularly suitable flatsheet adsorbent filtration medium is commercially available as PLEKX®from KX Industries, L.P., Orange, Conn. The flat sheet filtration mediummay contain hydrophilic or hydrophobic particles that can also betreated with the microbiological interception enhancing agent, althoughnot necessary, and immobilized on a substrate to provide addedmicrobiological interception capabilities in addition to that providedby the microbiological interception enhanced filter medium. At least oneadsorbent layer is preferably placed upstream from the microbiologicalinterception enhanced filter medium to reduce the deleterious effects ofNOM on the microbiological interception enhanced filter medium. Themicrobiological interception enhanced filter medium can serve as one ofthe substrates used to support the adsorbent used to filter NOM from theinfluent fluid. For example, the upper layer of the PLEKX® structure canbe a particulate prefilter. The core of the PLEKX® composite can beprimarily composed of an adsorbent with a high affinity for NOM, and thelower, downstream layer can be the microbiological interception enhancedfilter medium. The layers can be bonded into a single cohesive compositestructure using the PLEKX® process described in the above-mentionedpatents. The result is a hgh dirt capacity filter structure thatprovides chemical, particulate, and microbiological interception in asingle material. The core of the PLEKX® structure can include a widerange of ingredients useful for the adsorption of chemical contaminants.

2. GAC Filter Medium as an Adsorbent Prefilter

The microbiological interception enhanced filter medium may also be usedin conjunction with a bed of granular adsorbent such as, for example, agranular activated carbon (GAC) bed. The granular bed filter should beplaced upstream from the microbiological interception enhanced filtermedium to remove any charge-reducing contaminants, such as NOM, from theinfluent prior to contacting the charged microporous filter medium.

3. Solid Composite Block Filter Medium as an Adsorbent Prefilter

The microbiological interception enhanced filter medium may also be usedin conjunction with a solid composite block filter medium, preferablycomprising activated carbon, placed upstream from the microbiologicalinterception enhanced filter medium to remove any charge-reducingcontaminants, such as NOM, from the influent prior to contact with themicrobiological interception enhanced filter medium. The activatedcarbon block may include, but is not limited to, such materials asactivated alumina, zeolites, diatomaceous earth, silicates,aluminosilicates, titanates, bone char, calcium hydroxyapatite,manganese oxides, iron oxides, magnesia, perlite, talc, polymericparticulates, clay, iodated resins, ion exchange resins, ceramics, andcombinations thereof to provide additional reduction of contaminantssuch as heavy metals, arsenic, chlorine, and to improve taste and odor.These materials, as well as the activated carbon, may be treated withthe microbiological interception enhancing agent prior to beingconverted into a solid composite by extrusion, compression molding orother processes known to one of skill in the art. Exemplary processesare described in U.S. Pat. Nos. 5,019,311, and 5,189,092. The solidcomposite block can contain an anion-exchange resin that is specificallyselected for its high capacity to adsorb NOM.

Complete Filtration Devices Combining Adsorbent Prefilters andMicrobiological Interception Enhanced Filter Medim

One particular embodiment of a filtration system of the presentinvention includes a composite filter medium, as described above,including the microbiological interception enhanced filter medium andthe adsorbent filtration medium. This device is designated to operate asa gravity flow device with a driving pressure of only a few inches watercolumn to a maximum of a few feet of water column. The composite filtermedium is forced to first pass through the adsorbent prefilter and thenthe microbiological interception layer. As shown in FIG. 1, an exemplaryfilter design incorporates the composite filter medium of the presentinvention in a filter housing 10 having a clam shell type enclosure.Filter housing 10 has a top portion 12 having an inlet 14, and a bottomportion 16 having an outlet 18. Residing within a sealed cavity definedby the top portion and bottom portion is the composite filter medium 20shown more accurately in the cross sectional view of FIG. 2. Top portion12 and bottom portion 16 may be formed from a single sheet of apolymeric material and folded over to provide a clam shellconfiguration.

To assemble the filter, composite filter medium 20 is cut intosubstantially the size and shape of the clam shell enclosure. Compositefilter medium 20 is secured into bottom portion 16 and top portion 12 isplaced over bottom portion 16 and compressed together. The top andbottom shell portions 12, 16 may be welded together creating a weldment22 around the entire periphery of filter medium 20. As illustrated inFIG. 2, there is shown a substantially impermeable interface between thetop and bottom portions and the composite filter medium in the regiondirectly adjacent weldment 22. Excess material on the clam shellenclosure and composite filter medium is simply cut off. It will beunderstood that other methods of sealing the filter medium within thefilter housing may be used such as, but not limited to, adhesives,mechanical clamps, and the like. Although the filter design has a clamshell enclosure, the filter design is not limited to such. Any enclosurethat may be sealed such that an influent will not bypass the filtermedium would be suitable.

In referring back to FIG. 2, the seal formed between composite filtermedium 20 and top portion 12 and bottom portion 16 is such that waterbeing filtered is forced to follow the path illustrated by arrows A andB, and cannot bypass composite filter medium 20. In fact, at theperiphery of composite filter medium 20, the pressure exerted by theseal increases the density of the filter medium so that contact time ofthe water being filtered with composite filter medium 20 in thisperipheral region is increased and filtration efficiency enhanced.

During production of the filter, assurances concerning the seal andassembly integrity may be obtained using a vision system, and gas oraerosol pulse testing. The gas or aerosol pulse test uses a tiny pulseof dilute butane or fog-oil smoke that is entirely adsorbed orintercepted by an intact filter, but will significantly penetrate adefective filter. Other off-line test procedures known to one of skillin the art may be used to methodically examine the quality of the sealbetween the filter medium and the enclosure.

The wall of the filter housing may be sufficiently thin and flexible sothat when the filter is contacted with water, the modest pressureproduced by the hydrostatic load of the incoming water causes topportion 12 and bottom portion 16 to bow away slightly from and provide aclearance space between the inner surface of top portion 12 and bottomportion 16, and composite filter medium 20. This clearance space assistsin distributing the water across the influent surface of compositefilter medium 20 and provides drainage of the effluent into outlet 18.

Referring to FIG. 3, there is shown a front plan view of a filtrationsystem 30 of the present invention useful in providing potable water ina gravity flow device that may be useful in developing countries wheresafe, potable water of suitable microbiological quality is scarce.Although water is discussed as the liquid influent, it is within thescope of the invention to contemplate the filtration of other liquids.Filtration system 30 has a first reservoir 35 that is a raw watercollection transport container. First reservoir 35 may be a bagconfiguration as shown constructed of a substantially leak proofmaterial such as a polymeric material, i.e., polyester, nylon, apolyolefin such as polyethylene, polyvinyl chloride, and multi-layerfilms of the like. For ease of use, first reservoir 35 may have areinforced opening and a handle 36 for carrying and hanging firstreservoir 35 to provide a pressure head during filtration. Preferably,first reservoir 35 has a resealable opening 37 that when closed providesa substantially water-tight seal. Such resealable openings are known toone of skill in the art or may include a threaded opening with ascrew-on cap.

First reservoir 35 is preferably equipped with an output hose 40 suchthat water stored in the reservoir may be drained for filtration andeventual use. Output hose 40 is preferably made with a food-safe gradeof flexible polymer. Output hose 40 may be opened and closed using asimple clamp. Output hose 40 may be permanently attached to firstreservoir 35 by ultrasonic welding or retained simply by friction.Output hose 40 preferably has an internal extension end 42 within firstreservoir 35 such that internal extension end 42 extends above thebottom of the first reservoir 35 to provide an area for capturingsediment that can settle prior to water filtration. By limiting theamount of sediment present in the influent prior to water filtration,the useful life of the filtration system is prolonged.

Output hose 40 connects first reservoir 35 to a filter 10, describedabove, including the composite filter medium of the present invention. Aclamp 45 may be fitted on output hose 40 at any point along the lengthof output hose 40. Such clamps are well known in the art and may be asimple one piece configuration made of a flexible polymer or metal. Whenthe clamp is in an open position, water from first reservoir 35 flowsfreely into filter 10. Filter 10 is removably connected to output hose40. The outlet of filter 10 is then connected to a second reservoir 50.Second reservoir 50 serves as a collection vessel for the filtered wateror effluent. Alternatively, filter 10 and second reservoir 50 may beconnected together via a second output hose (not shown). Secondreservoir 50 generally is equipped with a means for dispensing thefiltered water.

The above filtration system may be used as follows. A user takes firstreservoir 35, with or without output hose 40 attached thereto, to awater source. If output hose 40 is still attached to first reservoir 35,clamp 45 must be in a closed position or first reservoir 35 must besealed by other means. First reservoir 35 is filled with a quantity ofraw water and its opening again sealed while the user carries firstreservoir 35 back to a preferred location such as a residence. It ispossible that the raw water is contaminated with microorganisms andchemical contaminants and may not be potable. To facilitate filtration,first reservoir 35 is suspended or hung from a support means. Dependingupon any significant sediment present as evidenced by turbidity, the rawwater is allowed to remain suspended for a period of time sufficient forthe sediment to settle below the height of internal extension end 42 ofoutput hose 40 within first reservoir 35. Of course, should the water berelatively clear, there is no need to suspend first reservoir 35 forsuch a period of time. Output hose 40 is attached to first reservoir 35,if previously detached, and secured to filter 10. Filter 10 is securedto second reservoir 50 for collecting the filtered water. Clamp 45 isthen placed in an open position and the water is allowed to flow intofilter 10 wherein the water once treated through composite filter medium20, is rendered potable, and collected in second reservoir 50. Topreserve the potability of the filtered water, the surfaces of secondreservoir 50 may be made from or treated with a disinfectant or with themicrobiological interception enhancing agent. Preferably, thedisinfectant used would not alter or affect the taste of the water.

Typical water flow rates are about 25 to about 100 ml/minute for adevice equipped with a filter of about 3″5″ size and operated at about6″ water column pressure. This provides one liter of potable water inabout 10 to 40 minutes having at least about 6 log reduction in bacteriaand at least about 4 log reduction in viral contaminants. Continual useof filter 10 will likely develop, by progressive deposition thereon, alayer of particles that will slow the flow rate until the filtrationprocess takes an unacceptable amount of time. Although the flow rate isdiminished, the filter will maintain its microbiological interceptioncapabilities for an extended period.

Another gravity flow device incorporating a filter medium of the presentinvention includes an exemplary carafe design as illustrated in FIG. 4for filtering, storing and dispensing filtered water or other fluids.Although the carafe shown is primarily round, the carafe 60 may assumeany shape depending upon its use and environment, and is a matter ofdesign choice. A basic carafe has a housing 62 with a handle 64 andcover 66. Carafe 60 is divided into a lower reservoir or storage chamber68 and an upper reservoir 78 that are enclosed by lid 70 and cover 66located within housing 62. Spout 72 facilitates the removal of filteredwater through outlet 74 of storage chamber 68.

Upper reservoir 78 and storage chamber 68 are separated by partition 80that is provided with a filter receiving receptacle 85 having an opening(not shown) in the bottom thereof. In one embodiment, a flat compositefilter medium 76 of the present invention is placed into filterreceiving receptacle 85 with a water tight seal to segregate upperreservoir 78 and storage chamber 68. Placement of filter medium 76 intofilter receptacle 85 may be accomplished using means known to one ofskill in the art including, but not limited to, a snap or hingedmechanism. Filter medium 76 is preferably manufactured as a replaceablecartridge. Other features of the carafe design may be incorporated intothe present invention without departing from the scope of the invention.The filter medium may comprise any microporous structure having a meanflow path of less than about 1 micron and so treated as to provide atleast about 4 log reduction of microbiological contaminants smaller thanthe mean flow path of the filter medium. Preferably, the filter mediumhas a volume of less than about 500 cm³ and has an initial flow rate ofgreater than about 25 ml/minute.

A user would pour raw water into upper reservoir 78 and allow the rawwater to pass through filter medium 76 under the influence of gravity.Filtered water is collected in storage chamber 68. As the raw waterpasses through the filter medium of the present invention withsufficient contact time, the filter medium renders the water potable byproviding a high titer reduction of microorganisms. The log reductionvalue (LRV) of microorganisms is dependent upon the contact time of thefilter medium with the flowing water. To provide about 8 log reductionvalue of microorganisms, the required contact time is about 6 to about10 seconds.

Carafe 60 may also have an indicator (not shown) that allows a user tokeep track of the age of the filter to gauge when the useful life of thefilter medium has been expended. Other types of indicators may also beused such as an indicator for indicating the number of refills of carafe60, for measuring the volume of water or liquid that passes through thefilter medium, and the like.

Other Filtration Systems

A filter medium of the present invention, in particular, the compositefilter medium, may also be incorporated into a point-of-use applicationsuch as a sports bottle design for use as a personal water filtrationsystem operating under a slight pressure, about 1 psi. A suitable sportsbottle design is disclosed in International Patent Application No. WO01/23306 wherein the filter medium may be incorporated into the filterreceptacle of the sports bottle.

For other point-of-use applications, the microbiological interceptionenhanced filter medium of the present invention may further beincorporated into end-of-tap (EOT), under-sink, counter-top, or othercommon consumer or industrial filtration systems and configurations foruse in pressurized systems. The filter system may include a prefiltercomprising a bed of adsorbent particles or a solid adsorbent compositeblock. The microbiological interception enhanced filter medium can be apleated or a spiral wound construction, or formed into a thick mat byvacuum formation on a suitable mandrel to create a wet-formed ordry-formed cartridge.

EXAMPLES

The following examples are provided to illustrate the present inventionand should not be construed as limiting the scope of the invention.

Porometry studies were performed with an Automated Capillary FlowPorometer available from Porous Materials, Inc., Ithaca, N.Y. Parametersdetermined, using standard procedures published by the equipmentmanufacturer, include mean flow pore size and gas (air) permeability.The flow of air was assayed at variable pressure on both the dry and wetfilter medium. Prior to wet runs, the filter medium was initiallyimmersed in silicon oil for at least 10 minutes while held under highvacuum.

Zeta or streaming potential of various filter media was determined usingstreaming potential and streaming current measured with a BI-EKAElectro-Kinetic Analyzer available from Brookhaven Instruments, ofHoltsville, N.Y. This instrument includes an analyzer, a flat-sheetmeasuring cell, electrodes, and a data control system. The analyzerincludes a pump to produce the pressure required to pass an electrolytesolution, generally 0.0015M potassium chloride, from a reservoir,through the measuring cell containing a sample of the filter mediumdescribed herein. Sensors for measuring temperature, pressure drop,conductivity and pH are disposed externally of the cell. In accordancewith this method the electrolyte solution is pumped through the porousmaterial. As the electrolyte solution passes through the sample, adisplacement of charge occurs. The resulting “streaming potential and/orstreaming current” can be detected by means of the electrodes, placed ateach end of the sample. The zeta (streaming) potential of the sample isthen determined by a calculation according to the method of Fairbrotherand Mastin that takes into account the conductivity of the electrolyte.

Bacterial challenges of the filter media were performed usingsuspensions of Escherichia coli of the American Type Culture Collection(ATCC) No. 11775 to evaluate the response to a bacterial challenge. Theresponse to viral challenges was evaluated using MS-2 bacteriophage ATTCNo. 15597-B1. The Standard Operating Procedures of the ATCC were usedfor propagation of the bacterium and bacteriophage, and standardmicrobiological procedures, as well known in the art, were used forpreparing and quantifying the microorganisms in both the influent andeffluent of filters challenged with suspensions of the microbiologicalparticles.

Examples 1-3

Filter Medium Made with Untreated Lyocell Fibers (Comparative)

Filter medium made from untreated lyocell fibers having a mean flow pathof about 0.3 to about 0.6 microns were prepared in accordance with thefollowing method.

Dry EST-8 binder fibers having a weight of 0.45 g, commerciallyavailable from MiniFibers, Inc., was fully dispersed in 1.0 L ofdeionized water in a kitchen style blender on a pulse setting.Fibrillated lyocell fibers with a Canadian Standard Freeness of 45 andhaving a dry weight of 120.0 g were added as wet pulp to the dispersedbinder fibers. The dispersed fiber mixture was blended for another 15seconds. The fiber mixture was poured into a larger industrial Waringblender with an additional 1.0 L of deionized water and blended for anadditional 15 to 30 seconds. The fiber mixture was poured into a30.5×30.5 cm² stainless steel FORMAX® paper deckle filled with about12.0 L of deionized water and fitted with a 100 mesh forming screen. A30×30 cm² stainless steel agitator plate having 60 holes of 2 cm indiameter was used to plunge the fiber mixture up and down from top tobottom about 8 to 10 times. The water was removed from the fiber mixtureby pulling a slight vacuum below the deckle to cause the fibers to formon the wire. Once the bulk of the water is removed, supplementaldewatering is accomplished with a vacuum pump to remove additionalexcess moisture and to create a relatively smooth, flat, fairly thinpaper-like sheet. The resulting sheet is separated from the screen andcombined with a blotter sheet on both top and bottom. The combination ofsheets is gently rolled with a 2.27 kg marble rolling pin to removeexcess water and smooth out the top surface of the sheet. The sheet isthen placed between two fresh and dry blotter sheets and placed on aFORMAX® sheet dryer for about 10 to about 15 minutes at about 120° C.The dried filter medium is separated from the blotter sheets anddirectly heated on the FORMAX® sheet dryer for about 5 minutes on eachside to activate the dry binder fibers.

Table I shows the porometry and air permeability test results performedon filter medium made from untreated lyocell fibers of varyingthicknesses made using the above process.

TABLE I Mean Flow Path and Porometry of Filter Medium Made WithUntreated Lyocell Fibers Sample Thickness Mean Flow Path GasPermeability Example # (mm) (μm) (L/cm² at 1 psi) 1 0.45 0.3804 5.48 20.66 0.6708 4.50 3 0.63 0.4316 5.30

The resulting filter medium made with untreated lyocell fibers had areproducible streaming potential of about −9.0 millivolts.

Example 4

Filter Medium Made with Lyocell Fibers Treated with the MicrobiologicalInterception Enhancing Agent

To a blender were added 12.0 g dry weight lyocell fibers as a 10% byweight wet pulp having a Canadian Standard Freeness of about 45, 0.45 gSHORT STUFF® EST-8 binder fibers, and 1.0 L deionized water. The mixturewas blended until the fibers were fully dispersed. To the blender wasadded 3.0 ml of MERQUAT® 100 as a 30% aqueous solution and the fibersblended with the MERQUAT® 100 for about 10 seconds and left to stand forat least about 6 hours. After about 6 hours, the fibers were poured intoa standard 8 inch Brit jar fitted with a 100 mesh forming wire andexcess water removed under vacuum. The resulting pulp sheet was rinsedwith 500 ml of deionized water. The excess water was again removed byvacuum.

A dilute silver nitrate solution was poured uniformly over the pulpsheet to provide full exposure and saturation, providing about 0.1425 gof silver per sheet. The silver nitrate solution was left on the pulpsheet for at least about 15 minutes and excess water removed undervacuum pressure. The silver-treated pulp sheet was then torn into smallpieces and placed in a WARING® blender and re-dispersed in 2.0 L ofdeionized water. A second 3.0 ml portion of the MERQUAT® 100 solutionwas added to the dispersion and the mixture blended for about 10 minutesand the contents poured into a 30.5×30.5 cm² stainless steel FORMAX®paper deckle fitted with a 100 mesh forming screen. Paper-like sheets ofthe microbiological interception enhanced filter medium were made in thesame manner as the untreated lyocell filter media described in Examples1 to 3.

The zeta potential of the filter medium was consistently greater thanabout +10 millivolts at a pH of about 7.0.

Examples 5-23

Comparison of Microbiological Interception with the MicrobiologicalInterception Enhanced Filter Medium of the Present Invention and theUntreated Lyocell Filter Medium

Sheets of fibrillated lyocell filter medium either untreated or treatedwith MERQUAT® 100 and silver, as described in Examples 1 to 4, werefolded twice and cut into standard cone-shaped funnels and placed intosmall sterilized glass funnels. Deionized water was used to pre-wet eachfilter medium. Approximately 125 ml of various microbiologicalchallenges were poured through the filters and the effluents collectedin sterile 250 ml Erlenmeyer flasks. The effluents were subjected toserial dilution in duplicate and plated on petri dishes followingstandard laboratory procedures as required for each organism and leftovernight in 37° C. heated incubators. The next day all test resultswere recorded. Table II summarizes the log reduction values of a seriesof tests run using microbiological challenges made with de-ionizedwater.

TABLE II LRVs of Filter Media Made With Treated And UntreatedFibrillated Lyocell Fibers Ex E. coli LRV E. coli LRV Ex MS2 LRV MS2 LRV# (Treated) (Untreated) # (Treated) (Untreated) 5 9.2 — 14 7.47 — 6 9.2— 15 7.47 — 7 9.2 — 16 7.47 — 8 9.2 — 17 7.76 — 9 9.2 — 18 7.76 — 10 9.2— 19 7.76 — 11 9.4 <1.0 20 8.58 <1.0 12 7.65 <1.0 21 8.58 <1.0 13 9.98<1.0 22 8.67 <1.0 23 8.19 <1.0 — = Minimal to no reduction.

As illustrated in Table II, the filter medium made from lyocell fiberstreated with MERQUAT® 100 and silver provided significantmicrobiological interception capabilities as compared to filter mediummade from untreated lyocell fibers. The efficacy of the microbiologicalinterception enhanced filter medium when challenged with MS2 viralparticles illustrates that a filtration system of the present inventionwould prove effective in removing nano-sized pathogens such as viruses.

Examples 24-27

Microbiological Interception Capability of the Filter Medium Made withTreated Lyocell Fibers in the Presence of Polyanionic Acids

As discussed above, NOM such as polyanionic acids reduce the positivezeta potential and, thereby, reduce the efficacy of the microbiologicalinterception enhanced filter medium. After exposure to 500 ml humic acid(0.005 g/1.0 L H₂O), the zeta potential of the microbiologicalinterception enhanced filter medium decreased from +14.1 to −14.4.Likewise, after exposure to 500 ml fulvic acid (0.005 g/1.0 L H₂O), thezeta potential of the microbiological interception enhanced filtermedium decreased from +10.1 to −8.9. Examples 24 to 27 show thereduction in microbiological interception capabilities of the filtermedium made with lyocell fibers treated with MERQUAT® 100 and silver inthe presence of humic and fulvic acid solutions.

Small discs of the filter medium treated with MERQUAT® 100 and silverwere folded and placed in small sterilized glass funnels to form afilter and pre-wetted with de-ionized water. Challenge solutions of E.coli and MS2 viral particles were made with humic acid and fulvic acid,respectively. Approximately 125 ml of the challenge solutions werepoured through the filters and the effluent collected in sterile 250 mlErlenmeyer flasks. The effluent was diluted and plated on petri dishesfollowing standard laboratory procedures. Log reduction values of E.coli and MS2 viral particles are summarized in Tables III and IV below.

TABLE III LRVs Of The Microbiological Interception Enhanced Filter MediaIn The Presence Of Fulvic Acid Ex # E. coli (LRV) MS2 (MRV) 24 4.68 4.23

TABLE IV LRVs Of The Microbiological Interception Enhanced Filter MediaIn The Presence Of Humic Acid Ex# E. coli (LRV) MS2 (MRV) 25 3.78 4.2326 3.02 1.64 27 6.73 3.58

Clearly, the LRVs of the microbiological interception enhanced filtermedia in the presence of NOM are significantly lower than the 7 to 9 logreduction of E. coli and MS2 absent NOM interference as shown in TableII.

Examples 28-46

Microbiological Interception Capability of the Filter Medium Made withTreated Lyocell Fibers and an Adsorbent Layer in the Presence ofPolyanionic Acids

In order to decrease the impact of NOM on the filter medium as shown inExamples 24 to 27, an adsorbent prefilter was added to the filter toremove or trap the NOM in the influent prior to contact with the filtermedium. The adsorbent layer is PLEKX® made with 600 g/m² of finelyground coal-based activated carbon having a surface area of 1000 m²/g,and is commercially available from KX Industries, L.P.

A composite filter medium combining two (2) layers of a filter mediummade with the microbiological interception enhanced filter medium andone (1) PLEKX® layer was fitted in ceramic Buchner funnels over a metaldrainage screen. The three (3) layers were secured in each Buchnerfunnels with a hot melt adhesive to prevent any bypass of the influent.A head pressure of water about 5 cm in depth was maintained in theBuchner funnel at all times. The filters of examples 28 to 34 werecharged with sterile deionized water prior to the microbiologicalchallenge and were not exposed to either humic or fulvic acids. Resultsshown in Table V below show that the efficacy of the composite filtermedium with the addition of the adsorbent layer is similar to theresults shown in Table II above.

The filters of examples 35 to 40 were charged with 500 ml of a humicacid solution (0.005 g/l L H₂O) prior to the microbiological challenge.Results are shown in Table VI below. The filters of examples 41 to 46were charged with 500 ml of a fulvic acid solution (0.005 g/1 L H₂O)prior to the microbiological challenge. Results are shown in Table VIIbelow.

TABLE V LRVs Of Filter Media Made With Fibrillated Lyocell FibersTreated With MERQUAT ® 100 And Silver With PLEKX ® Absent NOMInterference Ex # E. coli LRV Ex # MS2 LRV 28 7.89 31 8.06 29 7.89 328.06 30 7.89 33 8.49 34 8.49

TABLE VI LRVs Of Filter Media Made With Fibrillated Lyocell FibersUntreated And Treated With MERQUAT ® 100 And Silver With PLEKX ® In ThePresence Of Humic Acid Ex # E. coli LRV Ex # MS2 LRV 35 8.75 38 8.53 368.75 39 8.53 37 8.75 40 8.53

TABLE VII LRVs Of Filter Media Made With Fibrillated Lyocell FibersUntreated And Treated With MERQUAT ® 100 And Silver With PLEKX ® In ThePresence Of Fulvic Acid Ex # E. coli LRV Ex # MS2 LRV 41 8.85 44 7.77 428.85 45 7.77 43 8.85 46 7.77

The data shows that the use of an adsorbent prefilter such as PLEKX®,placed upstream from the microbiological interception enhanced filtermedium, maintained or improved the microbiological interceptioncapabilities of the filter medium by removing the NOM in the influentbefore the influent contacted the microbiological interception enhancedfilter medium. The adsorbent prefilter medium does not need to betreated with the microbiological interception enhancing agent tomaintain the efficacy of the microbiological interception enhancedfilter medium. It may be a cost saving measure not to treat theadsorbent prefilter medium. Thus, a composite filter medium includingthe microbiological interception enhanced filter medium and an adsorbentlayer positioned upstream from the microbiological interception enhancedfilter medium would be robust enough to withstand interference from NOM.

Examples 47-48

E. Coli Challenges of a Filtration System of the Present Invention

Two filtration systems of the present invention, as shown in FIG. 3,including a composite filter medium comprising two (2) layers of anadsorbent filter medium, PLEKX® made with 600 g/m² of coal-basedactivated carbon having a surface area of 1000 m²/g, and a single layerof the microbiological interception enhanced filter medium made fromtreated fibrillated lyocell fibers as described in Example 4 wereassembled using the clam shell filter design of FIGS. 1 and 2 describedabove. A supporting layer of PLEKX® was placed in the bottom of eachfilter housing and glued into place using an ethylene-vinyl acetate(EVA) hot melt. The layer of microbiological interception enhancedfilter medium was glued to the first PLEKX® layer, followed by a secondPLEKX® layer that was also glued into place atop the microbiologicalinterception enhanced filter medium. This configuration uses only one ofthe PLEKX® layers as an adsorbent prefilter, while the other PLEKX®layer serves primarily as a support for the microbiological interceptionenhanced filter medium. The outside edges of the housing were also gluedand pressed firmly together to prevent any bypass leakage to the outsideof the housing. The dimensions of active filter area within the boundarydefined by the hot melt material was between 5 cm to 6 cm wide and 8 cmto 10 cm long, providing an active filter area of between 40 cm² and 60cm². While hot melt was used during this prototype testing, filterassembly using ultrasonic or other welding methods may be applied duringcommercial production.

A 0.635 cm (0.25 inch) inside diameter hose was attached to the inlet ofthe filter housing using a plastic fitting and glued securely intoplace. The outlet of the filter was open to allow fluid to exit thefilter housing. The hose attached to the filter inlet was attached to aglass Pyrex funnel to produce a total inlet water column ofapproximately 30 cm to 60 cm. Test suspensions were poured into thefunnel to challenge the filter with various organisms.

Approximately 500 ml of de-ionized water was poured through thefiltration system to pre-wet the filter medium inside the housing. ForE. coli testing, a hose and funnel with a combined height of 60 cm wasused to provide head pressure. The flow rate at this influent pressurewas 70 ml/min. A challenge suspension of E. coli was poured through thesystem and the effluents collected in sterile 250 ml Erlenmeyer flasks.The effluents were subjected to serial dilution in duplicate and platedon petri dishes following standard laboratory procedures and leftovernight in 37° C. heated incubators. The next day all test resultswere recorded and these are listed in Table VIII below.

TABLE VIII Microbiological Challenges Of A Filtration System Of ThePresent Invention With E. coli # of colonies Ex # No. of E. coli inChallenge forming/plate LRV 47 8.4 × 10⁸ 0 8.92 48 8.4 × 10⁸ 0 8.92

Thus, a filtration system of the present invention utilizing a compositefilter medium including a PLEKX® prefilter and the microbiologicalinterception enhanced filter medium will provide greater than 8.5 logreduction of E. coli at a flow rate of approximately 1 to 2ml/minute·cm².

Example 49-51

MS2 Challenges of a Filtration System of the Present Invention

Three filters were constructed in a similar fashion as for the E. colichallenge as described in examples 47 and 48 above, for determining theviral interception capability of a filtration system of the presentinvention. In two filters, Examples 49 and 50, a layer of netting wasinstalled at the bottom, effluent side, of the filter housing, followedby a layer of the microbiological interception enhanced filter medium,followed by a single top layer of PLEKX® made with 600 g/m² ofcoal-based activated carbon having a surface area of 1000 m²/g. For thethird filter, Example 51, the plastic netting was replaced with a metal100 mesh screen as the bottom support layer. For the MS2 challenge, ahose and funnel of 30 cm was used to reduce the flow rate and allow forlonger contact time through the composite filter medium. De-ionizedwater was poured through the system to pre-wet the layers and verifythat the housing had no leaks. A flow rate of 38 ml/ minute was recordedfor the 30 cm high water column. After the de-ionized water exitedthrough the system, the MS2 challenge solution was poured through thesystem. The effluent was collected in sterile Erlenmeyer flasks, dilutedand plated on Petri dishes following standard procedures for MS2 andleft overnight. The next day all test results were recorded and listedin Table IX below.

TABLE IX Microbiological Challenges Of The Filter With MS2 Bacteriophage# of colonies Ex # No. of MS2 in Challenge forming/plate LRV 49 6.12 ×10⁸ 0 8.78 50 6.12 × 10⁸ 0 8.78 51 6.12 × 10⁸ 0 8.78

A filtration system of the present invention utilizing a compositefilter medium including a PLEKX® prefilter and the microbiologicalinterception enhanced filter medium is shown to provide greater than 8.5log reduction of MS2 at a flow rate of approximately 0.75 ml/minute·cm².

Examples 52 and 53

Long Term MS2 Challenges of a Filtration System of the Present Invention

These examples assess the effectiveness of a filtration system of thepresent invention when challenged with MS2 bacteriphage and having acomposite filter medium including two (2) layers of the microbiologicalinterception enhanced filter medium and two (2) layers of PLEKX® asdescribed earlier.

Two filtration systems of the present invention were prepared bysecuring a 100 mesh screen inside a filter enclosure as shown in FIGS. 1and 2. Two layers of the microbiological interception enhanced filtermedium were placed atop the mesh screen followed by two layers ofPLEKX®. Each layer was glued securely in place to prevent bypass. Thefilter enclosure was sealed with the glue as well. A 0.635 cm (0.25inch) inner diameter hose was attached securely to the inlet of thefilter housing. The outlet of the filter housing was open to allow thepassage of fluid. A funnel was securely attached to each filter toprovide one with a 25.4 cm (10 inches) water column, and the otherfilter with a 10.2 cm (4 inches) water column for testing ofmicrobiological challenges.

Deionized water, approximately 500 ml, was passed through eachfiltration system to pre-wet the filter medium and verify that no bypasswas occurring. Subsequently 500 ml of an MS2 challenge, prepared indeionized water, was passed through each system. The effluents werecollected in sterile Erlenmeyer flasks, diluted and plated on Petridishes following standard procedures for the organism and leftovernight. After 24 hours, an additional 500 ml of deionized water waspassed through the system followed by another 500 ml MS2 challenge. Thisprotocol was continued every 24 hours until the filter media no longerprovided an LRV above 4. The results are shown in Tables X and XI below.

TABLE X Example 52: Efficacy Of A Filtration System Of The PresentInvention With A 25.4 cm Water Column Total Amount Time in Use No. ofMS2 in Flow Rate of H₂O (L) (hours) Challenge LRV (ml/min.) 1.0 0 2.84 ×10⁸ 8.45 28 2.0 24 4.93 × 10⁸ 7.97 32 3.0 48 4.57 × 10⁸ 8.66 32 4.0 724.55 × 10⁸ 7.52 36 5.0 96 1.76 × 10⁹ 5.65 38 6.0 120 1.39 × 10⁹ 5.66 387.0 144 1.48 × 10⁹ 3.03 36 8.0 168 1.56 × 10⁹ 2.22 30

TABLE XI Example 53: Efficacy Of A Filtration System Of The PresentInvention With A 10.2 cm Water Column Total Amount Time in Use No. ofMS2 in Flow Rate of H₂O (L) (hours) Challenge LRV (ml/min.) 1.0 0 2.05 ×10⁹ 9.31 12 2.0 24 2.16 × 10⁹ 9.33 15 3.0 48 1.46 × 10⁹ 9.16 15 4.0 721.05 × 10⁹ 9.02 17 5.0 96 1.52 × 10⁹ 9.18 16 6.0 120 1.31 × 10⁹ 9.12 137.0 144 1.19 × 10⁹ 9.08 13 8.0 168 1.32 × 10⁹ 8.23 13 9.0 192 8.67 × 10⁸8.93 16 10.0 216 1.34 × 10⁹ 9.13 10 11.0 240 1.10 × 10⁹ 9.04 11 12.0 2641.24 × 10⁹ 7.76 9 13.0 288 1.24 × 10⁹ 8.27 9 14.0 316 1.02 × 10⁹ 3.62 715.0 340 1.04 × 10⁹ 3.41 8 16.0 364 1.03 × 10⁹ 3.36 10 17.0 388 1.07 ×10⁹ 3.03 10

The useful life of the filtration system of Example 52 with a pressurehead of 25.4 cm provided an acceptable MS2 log reduction for 6.0 L ofwater for 120 hours. However, when the pressure head was 10.2 cm, as inExample 53, the useful life of the filtration systems was extended,providing acceptable log reduction values of MS2 for a volume of 13.0 Lof water and 364 hours. It is apparent that the flow rate will affectthe microbiological interception capabilities of the filtration system.From the results of Examples 52 and 53, a lower flow rate will providemore effective microbiological interception due to greater contact timeof the microorganisms with the filter medium.

Example 54

Long Term E. Coli Challenges of a Filtration System of the PresentInvention

This example assesses the effectiveness of a filtration system of thepresent invention having a composite filter medium including two (2)layers of the microbiological interception enhanced filter medium andtwo (2) layers of PLEKX® as described earlier.

Deionized water, approximately 500 ml, was passed through the filtrationsystem to pre-wet the filter medium and verify that no bypass wasoccurring. Subsequently, 500 ml of the E. coli challenge, prepared indeionized water, was passed through the filter. The effluent wascollected in a sterile Erlenmeyer flasks, diluted and plated on Petridishes following standard procedures for E. coli and left overnight.After 24 hours, an additional 500 ml of deionized was passed through thesystem followed by another 500 ml E. coli challenge. This protocol wascontinued every 24 hours until the filter medium no longer provided anLRV above 4. The results are shown in Table XII below.

TABLE XII Example 54: Efficacy Of A Filtration System Of The PresentInvention With A 25.4 cm Water Column Total Amount Time in Use No. of E.coli Flow Rate of H₂O (L) (hours) in Challenge LRV (ml/min.) 1.0 0 9.33× 10⁸ 8.99 28 2.0 24 7.86 × 10⁸ 8.89 32 3.0 48 2.86 × 10⁸ 8.46 27 4.0 721.35 × 10⁹ 8.37 21 5.0 96 1.18 × 10⁹ 8.07 17 6.0 120  8.4 × 10⁸ 7.38 187.0 144 1.09 × 10⁹ 4.95 12 8.0 168  3.6 × 10⁸ 3.50 16 9.0 192 6.13 × 10⁸3.61 12

The filtration system of Example 50 provided acceptable performanceafter 6.0 L of water had passed through the system at an average flowrate of about 24 ml/minute wherein the head pressure was caused by a25.4 cm water column.

While the present invention has been particularly described, inconjunction with a specific preferred embodiment, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives; modifications and variations as falling within the truescope and spirit of the present invention.

What is claimed is:
 1. A filter medium comprising: a microporousstructure having a mean flow path of less than or equal to about 1micron; and a microbiological interception enhancing agent comprising acationic metal complex comprising a cationic material adsorbed on atleast a portion of said microporous structure, having an associatedcounter ion therewith, capable of imparting a positive charge on atleast a portion of said microporous structure, and wherein abiologically active metal is caused to precipitate with at least aportion of the counter ion associated with the cationic material.
 2. Thefilter medium of claim 1 wherein said microporous structure comprises aplurality of nanofibers having a fiber diameter of less than about 1000nanometers.
 3. The filter medium of claim 2 wherein the nanofiberscomprise organic fibers, inorganic fibers, or a mixture thereof.
 4. Thefilter medium of claim 2 wherein the nanofibers comprise glass fibers.5. The filter medium of claim 2 wherein the nanofibers comprise polymerfibers.
 6. The filter medium of claim 5 wherein at least a portion ofthe polymer fibers are substantially fibrillated.
 7. The filter mediumof claim 5 wherein the nanofibers comprise cellulose fibers.
 8. Thefilter medium of claim 7 wherein at least a portion of the cellulosefibers are substantially fibrillated.
 9. The filter medium of claim 1wherein said microporous structure is a membrane comprising an organicmaterial, an inorganic material, or a mixture thereof.
 10. The filtermedium of claim 9 wherein the membrane comprises a polymer material. 11.The filter medium of claim 1 wherein said microbiological interceptionenhancing agent consists of a cationic metal complex wherein a cationicmaterial on a surface of said microporous structure has an associatedcounter ion therewith and wherein a biologically active metal is causedto precipitate with at least a portion of the counter ion associatedwith the cationic material.
 12. The filter medium of claim 11 whereinthe cationic material is adsorbed, chemically bonded or crosslinked toat least a portion of a surface of said microporous structure.
 13. Thefilter medium of claim 11 wherein the cationic material having a counterion associated therewith is selected from the group consisting ofamines, amides, quaternary ammonium salts, imides, benzalkoniumcompounds, biguanides, aminosilicon compounds, polymers thereof, andcombinations thereof.
 14. The filter medium of claim 11 wherein thecationic metal complex includes a biologically active metal selectedfrom the group consisting of silver, copper, zinc, cadmium, mercury,antimony, gold, aluminum, platinum, palladium, and combinations thereof.15. A filter medium of claim 1 further including an adsorbent prefilteradapted to remove charge-reducing contaminants from an influent prior tothe influent contacting said microporous structure.
 16. A filter mediumcomprising: a microporous structure having a mean flow path of less thanor equal to about 1 micron, wherein said microporous structure comprisesa plurality of nanofibers comprising substantially fibrillated lyocellfibers; and a microbiological interception enhancing agent comprising acationic metal complex capable of imparting a positive charge on atleast a portion of said microporous structure.
 17. A filter mediumcomprising: a microporous structure having a mean flow path of less thanor equal to about 1 micron, wherein said microporous structure comprisesa plurality of nanofibers comprising substantially of fibrillatedlyocell fibers, wherein at least a portion of the fibrillated lyocellfibers are about 1 millimeter to about 8 millimeters in length and havea diameter of less than or equal to about 1000 nanometers; and amicrobiological interception enhancing agent comprising a cationic metalcomplex capable of imparting a positive charge on at least a portion ofsaid microporous structure.
 18. A filter medium comprising: amicroporous structure having a mean flow path of less than or equal toabout 1 micron, wherein said microporous structure comprises a pluralityof nanofibers comprising substantially of fibrillated lyocell fibershaving a Canadian Standard Freeness of less than or equal to about 100;and a microbiological interception enhancing agent comprising a cationicmetal complex capable of imparting a positive charge on at least aportion of said microporous structure.
 19. A filter medium comprising: amicroporous structure having a mean flow path of less than or equal toabout 1 micron, wherein said microporous structure comprises a pluralityof nanofibers comprising substantially of fibrillated lyocell fibershaving a Canadian Standard Freeness of less than or equal to about 45;and a microbiological interception enhancing agent comprising a cationicmetal complex capable of imparting a positive charge on at least aportion of said microporous structure.
 20. A filter medium comprising: amicroporous structure having a mean flow path of less than about 1micron; an adsorbent prefilter medium containing activated carbon,activated alumina, zeolites, diatomaceous earth, silicates,aluminosilicates, titanates, bone char, calcium hydroxyapatite,manganese oxides, iron oxides, magnesia, perlite, talc, polymericparticulates, clay, iodated resins, ion exchange resins, ceramics, orcombinations thereof; and a microbiological interception enhancing agentcomprising a cationic metal complex capable of imparting a positivecharge on at least a portion of said microporous structure.
 21. A filtermedium comprising: a microporous structure having a mean flow path ofless than or equal to about 1 micron; and a microbiological interceptionenhancing agent comprising a cationic metal complex capable of impartinga positive charge on at least a portion of said microporous structure,wherein the cationic metal complex is formed by treating at least aportion of said microporous structure with a cationic materialcomprising a homopolymer of diallyl dimethyl ammonium halide followed byprecipitation of silver with at least a portion of the halide counterion associated with the homopolymer of diallyl dimethyl ammonium halide.22. A filter medium comprising: a microporous structure having a meanflow path of less than or equal to about 1 micron; and a microbiologicalinterception enhancing agent comprising a cationic metal complex capableof imparting a positive charge on at least a portion of said microporousstructure, wherein the cationic metal complex is formed by treating atleast a portion of said microporous structure with a cationic materialcomprising a homopolymer of diallyl dimethyl ammonium halide having amolecular weight of about 400,000 Daltons, followed by precipitation ofsilver with at least a portion of the halide counter ion associated withthe homopolymer of diallyl dimethyl ammonium halide.
 23. A filter mediumcomprising: a microporous structure having a mean flow path of less thanor equal to about 1 micron, wherein said microporous structureincorporates one or more materials selected from the group consisting ofactivated carbon, activated alumina, zeolites, diatomaceous earth,silicates, aluminosilicates, titanates, bone char, calciumhydroxyapatite, manganese oxides, iron oxides, magnesia, perlite, talc,polymeric particulates, clay, iodated resins, ion exchange resins,ceramics, and combinations thereof; and a microbiological interceptionenhancing agent comprising a cationic metal complex capable of impartinga positive charge on at least a portion of said microporous structure.24. A filter medium comprising: a microporous structure having a meanflow path of less than or equal to about 1 micron wherein saidmicroporous structure further includes a binder; and a microbiologicalinterception enhancing agent comprising a cationic metal complex capableof imparting a positive charge on at least a portion of said microporousstructure.
 25. A filter medium comprising: a microporous structurehaving a mean flow path of less than or equal to about 1 micron; and amicrobiological interception enhancing agent comprising a cationic metalcomplex capable of imparting a positive charge on at least a portion ofsaid microporous structure wherein said microbiological interceptionenhancing agent consists of a silver-amine-halide complex wherein acationic amine on a surface of said microporous structure has anassociated halide counter ion therewith and wherein silver is caused toprecipitate with at least a portion of the halide counter ion associatedwith the cationic amine.
 26. A filter medium comprising: a microporousstructure having a mean flow path of less than or equal to about 1micron; and a microbiological interception enhancing agent comprising acationic metal complex capable of imparting a positive charge on atleast a portion of said microporous structure, the cationic metalcomplex consisting of a silver-amine-halide complex wherein a cationicamine on a surface of said microporous structure has an associatedhalide counter ion therewith and wherein silver is caused to precipitatewith at least a portion of the halide counter ion associated with thecationic amine, the cationic amine comprising a homopolymer of diallyldimethyl ammonium halide having a molecular weight of greater than orequal to about 400,000 Daltons.